On 09/23/2010 01:40 PM, Balbir Singh wrote: > * Nathan Fontenot <nfont@xxxxxxxxxxxxxx> [2010-09-22 09:15:43]: > >> This set of patches decouples the concept that a single memory >> section corresponds to a single directory in >> /sys/devices/system/memory/. On systems >> with large amounts of memory (1+ TB) there are performance issues >> related to creating the large number of sysfs directories. For >> a powerpc machine with 1 TB of memory we are creating 63,000+ >> directories. This is resulting in boot times of around 45-50 >> minutes for systems with 1 TB of memory and 8 hours for systems >> with 2 TB of memory. With this patch set applied I am now seeing >> boot times of 5 minutes or less. >> >> The root of this issue is in sysfs directory creation. Every time >> a directory is created a string compare is done against all sibling >> directories to ensure we do not create duplicates. The list of >> directory nodes in sysfs is kept as an unsorted list which results >> in this being an exponentially longer operation as the number of >> directories are created. >> >> The solution solved by this patch set is to allow a single >> directory in sysfs to span multiple memory sections. This is >> controlled by an optional architecturally defined function >> memory_block_size_bytes(). The default definition of this >> routine returns a memory block size equal to the memory section >> size. This maintains the current layout of sysfs memory >> directories as it appears to userspace to remain the same as it >> is today. >> >> For architectures that define their own version of this routine, >> as is done for powerpc in this patchset, the view in userspace >> would change such that each memoryXXX directory would span >> multiple memory sections. The number of sections spanned would >> depend on the value reported by memory_block_size_bytes. >> >> In both cases a new file 'end_phys_index' is created in each >> memoryXXX directory. This file will contain the physical id >> of the last memory section covered by the sysfs directory. For >> the default case, the value in 'end_phys_index' will be the same >> as in the existing 'phys_index' file. >> > > What does this mean for memory hotplug or hotunplug? > Memory hotplug will function on a memory block size basis. For architectures that do not define their own memory_block_size_bytes() routine, they will get the default size and everything will work the same as it does today. For architectures that define their own memory_block_size_bytes() routine and have multiple memory sections per memory block, hotplug operations will add or remove all of the memory sections in the memory memory block. -Nathan -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>